A liquid crystal display device has been developed from various aspects so as to respond to demands for higher function and lower power consumption. For example, a liquid crystal display device has been developed in which (i) a region (reflective region) where a reflective film is provided and (ii) a region (transmissive region) where no reflective film is provided are provided in a dot of each pixel and which is capable of switching modes of displaying an image, a moving picture, or the like. Such a liquid crystal display device includes an upper substrate and a lower substrate. A color filter is provided on the upper substrate or the lower substrate. Furthermore, a light source such as a backlight is provided on the lower substrate's side.
In a bright place, the liquid crystal display device employs a reflective mode in which the reflective region is used. The reflective mode is such that: external light which enters the liquid crystal display device from above the upper substrate is reflected in the reflective region and the light thus reflected is emitted toward the upper substrate, thereby an image, a moving picture, or the like is displayed on a display screen of the liquid crystal display device. On the other hand, in a dark place, the liquid crystal display device employs a transmissive mode in which the transmissive region is used. The transmissive mode is such that: light which is emitted from the backlight and enters the liquid crystal display device from above the lower substrate is transmitted through the transmissive region, and the light thus transmitted is emitted toward the upper substrate, thereby an image, a moving picture, or the like is displayed on the display screen of the liquid crystal display device. This allows the backlight to consume lower power since the liquid crystal display device uses the light emitted from the backlight only in a dark place.
However, in the reflective mode, the light emitted from the liquid crystal display device is transmitted through the color filter two times. This is because the external light which enters the liquid crystal display device from above the upper substrate is reflected in the reflective region and the light thus reflected is emitted toward the upper substrate. On the other hand, in the transmissive mode, the light emitted from the liquid crystal display device is transmitted through the color filter one time. This is because the light which is emitted from the backlight and enters the liquid crystal display device from above the lower substrate is transmitted through the transmissive region, and the light thus transmitted is emitted toward the upper substrate. For this reason, there occurs difference in color density between the light emitted from the reflective region and, the light emitted from the transmissive region in a case where the reflective region and the transmissive region are made of an identical resist material.
In order to deal with this problem, Patent Literature 1 discloses a liquid crystal display device in which a non-colored region is provided in a color filter in a reflective region.
According to the liquid crystal display device disclosed in Patent Literature 1, light which is obtained in a reflective mode by being transmitted through the color filter two times is light in which (i) uncolored light which is transmitted through the non-colored region and (ii) colored light which is transmitted through a colored region are superposed. On the other hand, light which is obtained in a transmissive mode by being emitted from a backlight, thereafter being transmitted through the color filter one time is all transmitted through the colored region and becomes colored light. As described earlier, it is possible to close a difference in color density between the light which is obtained in the reflective mode by being transmitted through the color filter two times and the light which is obtained in the transmissive mode by being transmitted through the color filter one time. Accordingly, the liquid crystal display device disclosed in Patent Literature 1 allows an obtainment of a display with high visibility.
In recent years, a liquid crystal display device has also been developed which includes a light sensor element provided in each pixel so as to have an optical input function. The liquid crystal display device with the optical input function is capable of carrying out image pickup operation and control operation in addition to display operation. Specifically, it is possible to realize a liquid crystal display device which has a touch panel function, a scanner function, a camera function, or a fingerprint sensor function. According to the liquid crystal display device, it is also possible to determine that it is dark around the liquid crystal display device and to activate a backlight in a case where the light sensor element receives a small amount of light.
Patent Literature 2 discloses a liquid crystal display device which includes: (i) a light sensor element provided in a reflective display section in which a reflective electrode is provided and (ii) an opening provided in a region which corresponds to the light sensor element in a color filter. According to the liquid crystal display device disclosed in Patent Literature 2, light which enters the light sensor element passes through the opening. Namely, the light which enters the light sensor element is not absorbed in the color filter, and it is therefore possible to provide a liquid crystal display device in which a decrease in sensitivity of the light sensor element is prevented.
This is explained below with reference to FIGS. 6 and 7.
FIG. 6 is a plan view of a pixel including a transmissive region and a reflective region, the pixel including a light sensor element provided in the reflective region. FIG. 7 is a cross-sectional view taken along the line B-B′ of FIG. 6.
A picture element 103 is constituted by (i) a pixel 103R in which a red color filter is provided, (ii) a pixel 103G in which a green color filter is provided, and (iii) a pixel 103B in which a blue color filter is provided (see FIG. 6). The pixel 103R, the pixel 103G, and the pixel 103B include respective transmissive regions and respective reflective regions. The respective reflective regions include respective openings 122b. Furthermore, the respective openings 122b include respective light sensor elements 114.
The picture element 103 includes a first substrate 111 and a second substrate 121 which are provided so as to face each other via a liquid crystal layer 117 (see FIG. 7). A light blocking film 112 is locally provided on the first substrate 111 in the reflective region so that the blocking film 112 positionally corresponds to a light sensor element 114. Moreover, an insulating film 113 is provided on the first substrate 111 so that the insulating film 113 covers the light blocking film 112. Further, the light sensor element 114 is provided right above the light blocking film 112 via the insulating film 113. Furthermore, an insulating film 115 is provided so as to cover the light sensor element 114, and a reflective electrode 116 is provided on the insulating film 115. In the reflective electrode 116, an opening region is provided right above the light sensor element 114.
Moreover, a color filter 122 is provided on the second substrate 121 facing the first substrate 111. An opening 122b is provided on the color filter 122 in the reflective region. The opening 122b is provided so as to face the light sensor element 114. Further, a transparent resin 123 for forming a multi gap is provided so as to cover the opening 122b. 
According to such an arrangement, the reflective electrode 116 reflects light reaching thereto via the second substrate 121, the color filter 122 and the liquid crystal layer 117, thereby display is carried out in the reflective mode. On the other hand, light which enters the light sensor element 114 from the second substrate 121 passes through the opening 122b. This prevents reduction in light intensity due to the color filter 122, and it is therefore possible to prevent a decrease in sensitivity of the light sensor element 114.
However, Patent Literature 2 includes the light sensor element 114 provided in the reflective region, and it is therefore necessary to secure a region in the reflective region in which region the light sensor element 114 is to be provided. For this reason, an area of the transmissive region becomes small since an area of the reflective region becomes large. This causes a problem of a decrease in aperture ratio of the transmissive region.
On the other hand, it may be an option to provide a light sensor element in the transmissive region. However, light which enters from outside enters the light sensor element through the color filter in this case. This causes a decrease in light receiving sensitivity of the light sensor element, as explained earlier. For this reason, it is necessary to increase an area of the light sensor element so as to increase a light receiving sensitivity of the light sensor element. This causes a problem of a decrease in aperture ratio of the transmissive region.